How to delete or replace images

Ok, so I have editing privileges now, and have a few questions.  The images now on the site (Famous Monsters Of Filmland) are all just scans found on the internet.  Mine are covers that have been painstakingly restored to pristine condition, and much higher resolution.  So, how exactly do I go about replacing the old ones with the new ones?  I see no sense having both of them on there, if one better represents the cover.  Do I contact the person who originally put them there?  Also, how do I go about replacing one of them that I put there, with a version that I have made some changes to?  Thanks in advance for any help.

Well, you need 5,000 (I think) points to change a main image. 
 
Removing Content - Used for removing covers for issues, like what you need done. Since there are only your cover and a lesser quality cover, yours will become the main image.
Main Picture Changing - Change the main picture of a character, team, thing, issue, etc.

Thanks for your reply, but even after reading all that stuff, I'm still not clear about whether or not I can replace an image that I posted with an improved image, or whether I need to request to have a moderator do it for me.  I have over 5,000 points. 

Thanks, but I know I can make my image the default image, I've done that.  What I need to know is if I can replace an image I've posted with an improved image.    If I posted the original, without the blessing of a moderator, it just makes sense to me that I should be able to replace that image if I deem it necessary. 

"Removing Content - Used for removing covers for issues, like what you need done. Since there are only your cover and a lesser quality cover, yours will become the main image."

@majinblackheart do you think you could delete a photo for me? i cant seem to do it